You can try this:
But, it will create a new account and your old files will still not be accessible.
Creating a new Admin on Mac Os X:
Here's how to reset your OS X password without an OS X CD.
the Working solution for me was to create a new admin
you can create new admin like this by deleting a specific file.
You need to enter terminal and create a new admin account:
2. Hold apple key + s key down after you hear the chime.
(command + s keys on newer Macs)
3. When you get text prompt enter in these terminal commands to create a brand new admin account (hitting return after each line):
mount -uw /
shutdown -h now
4. After rebooting you should have a brand new admin account. When you login as the new admin you can simply delete the old one and your good to go again!
Apple stores wont reset it for you. Computer shops may charge you $50 to $200 trying to reinstall the Mac and failing at the end.